It supplies 530,000 litres to Colombo each day.

The water level of Kelani River has gone up to 7.4 feet according to the Nagalagam Street water gauge, which is a high risk level of flooding.

A minor flooding occurs when the water level is at between three and five feet, high risk flooding when it is between five and nine feet, and a major flooding if it goes over nine feet.

The biggest flooding in recent history occurred in 1989, said irrigation director Hema Hettiarachchi.

Tributaries of the Kelani - Gurugoda Oya, Seethawaka Oya and Kehelgamu Oya - are all at overflow level, while the water level of the Kelani could go up further, she said.

It will take several days for the flooding in the Kelani valley area to recede, as its water level will depend on the amount of rainfall in the central hills.

At a media briefing, Colombo division irrigation director G.K. Padmakeerthi said sandbags were being used to prevent the breach of the banks of the Kelani.

However, there is no danger of the dams giving way, he said.